1. Machines make work easier.
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Machines make work easier.
2.1

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Mechanical Advantage
-  A winding road is actually a series of inclined planes with switchbacks, which allow cars to drive up a steep hill.
 Mechanical Advantage – amount by which a machine can multiply a force. (or how much the machine does the work to move an object)
also called the force ratio

3. Mechanical Advantage Definitions:
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Mechanical Advantage
Definitions:
Input Force – force applied to the machine.
Output Force – force the machine applies to the object.
Force is measured in Newtons (N).
(1 kg = 9.81 N of force)
Mechanical Advantage= Force output (N) Force Input (N)

4. Mechanical Advantage
MA > 1 = applied force is bigger than resulting force
Most simple machines work like this
MA = 1 = No advantage (both sides give equal amounts of force)
MA< 1 = resulting force is less than the applied force
Doesn’t necessarily mean the machine is flawed, but serves a different purpose
Ex. Screws have low MA. If if had a high MA, it would be useless

5. A Mechanical Advantage Less Than 1
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A Mechanical Advantage Less Than 1
 Useful for tasks that do not require a large output force.
Ex) Bicycle – the output force is used for speed.
MA greater than one requires more work
Ex. Pulleys, or pulling a rope has a MA of 2.

6. 1.     Calculate the mechanical advantage for a lever that has the following characteristics: (2 marks)
Input force: 200N
Output force: 550N

7. Mechanical Advantage Questions
Bill Nye – Mechanical Advantage

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Speed
 Speed – measures the distance an object travels in a given amount of time.
Speed= Distance (m)
Time(s)

10. 1) Calculate the speed of a person running the 400 m race in 55 seconds

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Speed Ratio
Speed Ratio – measure of how the speed of the object is affected by a machine.
SR describes how much faster the user is moving than the load is working (or how much effort you need to put into it to get out of it)
SR= Input Distance (m)
Output Distance (m)

12. 1.     Calculate the speed ratio for a lever that has the following characteristics: (2 marks)
·        Input distance: 45m
·        Output distance: 15m

13. Speed Ratio Questions

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Recall
** A machine can increase or change the direction of the force that you apply.
But, the cost is that the force the user applies must move farther than the load.

15. The Effect of Friction Friction – force that opposes motion.
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The Effect of Friction
 Friction – force that opposes motion.
- caused by the roughness of surfaces.
- As roughness of a surface increases so does the effect of friction.
Mechanical Advantage does NOT always equal Speed Ratio.
- Friction can affect MA, but not SR.
- Speed ratio represents the ideal mechanical advantage (No friction).

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Efficiency
- Friction creates HEAT, and must be released to protect the system.
Efficiency
Efficiency – measurement of how well a machine or device uses energy.
affected by friction.
most energy lost is unusable (ex. Heat).

17. Efficiency Efficiency= MA OR Output Energy SR Input Energy
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Efficiency
Efficiency= MA OR Output Energy
SR  Input Energy
Most complex machines are very inefficient: waste energy.
Ex) Car – 15% efficient.

18. 1.     Calculate the efficiency for a lever that has the following characteristics: (4 marks)
·        Input distance: 45m
·        Output distance: 15m
·        Input force: 200N
Output force: 550N

19. MA= Output force/Input force
=550N/200N
= 2.75
SR= Input distance/Output distance
= 45m/15m
= 3
E= MA/SR
= 2.75/3
=0.9166
=91.7%

20. Efficiency Questions

21. Formulas to know thus far:
MA= Output force/Input force
S=Distance/Time (m/s)
SR= Input distance/ output distance
Efficiency= MA/SR

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Homework!
C & R p. 286
2-5
Practice Questions